The overall objective of new application is to determine the role and mechanism of NADPH-related oxidative stress in Hyperhomocysteinemia (HHcy)-caused monocyte differentiation and endothelial dysfunction. The hypothesis to be tested in this proposal is that HHcy causes SAH accumulation, resulting in hypomethylative epigenetic modification on NADHP oxidase gene, leading to NADPH oxidase-related oxidative stress and inflammatory MC differentiation, contributing to vascular dysfunction. This project will study this hypothesis utilizing three linked specific aims. In Aim 1, they will characterize MC differentiation/adhesion, and vascular function/inflammation in HHcy mice. In Aim 2, they will examine the role and mechanism of NADPH oxidase activation and epigenetic modification in Hcy-induced MC differentiation in mouse primary splenocytes. In Aim 3, they will define the role of HHcy, SAH accumulation, DNA hypomethylation, and NADPH oxidase activation in inflammatory MC differentiation and vascular dysfunction in Tg-hCBS Cbs-/- mice. It is believed that completion of the specific aims of this proposal may provide important insights into the role of Hcy in CVD, and identify the underline mechanism.